Due to the fact that Group 15 elements have extra stable half-filled p orbitals electronic configurations, as compared to this Group 16 have:
higher electronic configuration
lower atomic and ionic radii
Higher electronegativity
lower ionisation enthalpy
Correct option (d) lower ionisation enthalpy
Ionisation enthalpy decreases down the group.It is due to increase in size.The elements of Group 16 have lower ionisation enthalpy values compared to those of Group 15 in the corresponding periods as group 15 elements have extra stable half-filled p orbitals electronic configurations and this is the reason for this.